Apparatus for synchronizing the output of a particle accelerator with a moving object



Dec. 3, 1957 T. M. DICKINSON APPARATUS FOR SYNCHRONIZING THE OUTPUT OF APARTICLE ACCELERATOR WITH A MOVING OBJECT Filed March 51, 1954 2Sheets-Sheet l a a N 0.7 M nw k c c r #m 0 NC 2 M N W mm A r u w w 0 WTMm c a r m A /u 7 7 c 5 mm 8 A s 3 T. M. DICKINSON 2,815,450 APPARATUSFOR SYNCHRONIZING THE OUTPUT OF A PARTICLE Dec. 3, 1957 ACCELERATOR WITHA MOVING OBJECT 2 Sheets-Sheet 2 Filed March 31, 1954 UVVVV m NNM W Q"WA/W" I I l I l I I l l I I I I l I i i M u/yigw ill-Is flator-ney niteStates Patent APPARATUS FOR SYNCHRONIZING THE OUTPUT OF A PARTICLEACCELERATOR WITH A MOV- ING OBJECT Theodore M. Dickinson, Schenectady,N. Y., assignor to General Electric Company, a corporation of New YorkApplication March 31, 1954, Serial No. 420,067

25 Claims. (Cl. 250-65) This invention relates to particle acceleratorsand their synchronization, and more particularly to the use of suchparticle accelerators to make stroboscopic X-ray pic tures orradiographs of a moving object.

It is well known that energy of the order of several million electronvolts or higher may be'imparted to charged particles such as electronsby accelerating the particles with a magnetic induction or electrostaticfield. One example of an apparatus for producing this result isdisimparted to the ch'arged particles by subjecting them to therepetitive action of a cyclically-varying electric field after they havebeen accelerated to a desired energy level by the above-mentionedbetatron apparatus. Suitable apparatus for achieving this purpose isdisclosed in U. S. Patent No. 2,485,409, granted on October 18, 1949 toH. C. Pollock and W. F. Westendorp and also assigned to the assignee ofthis invention. This latter apparatus is commonly referred to in the artas a synchrotron utilizing betatron start. It generally comprises meanssuch as a high frequency resonator coupled to the charged particleorbital path for applying a localized cyclically-varying electric fieldto accelerate the particles after they have ben pro-accelerated bybetatron action, and means for producing a time-varying magnetic guidefield traversing the locus of the orbital path for constraining theparticles thereto during the application of the electric field.

It is also common in the art, when using either of the above-mentionedforms of apparatus for accelerating particles, to employ iron coremagnets to provide suitable magnetic fields and fluxes. However, theiron cores of these magnets may saturate extremely rapidly since thecentral flux therethrough is approximately twice that present at theorbital path of the accelerated particles. As suggested by D. W. Kerstand R. Server in vol. 60 of the Physical Review, pg. 53 (1941), thissituation may be dealt with by biasing the core of the magnet with adirect current for producing an initial field that is opposite indirection to the final field. Thus the central flux can be made twiceits normal value without increasing the saturation of the iron. Particleaccelerators that utilize or do not utilize such direct currents arerespectively called biased or unbiased machines in the art.

Both biased and unbiased betatrons and synchrotrons can be used toproduce short bursts of X-rays, bursts that are short enough toadequately stop the motion of fast moving objects and produce a sharpimage upon a film. This may be done by diverting'the moving parti clesafter their acceleration has proceeded to the desired degree anddirecting them at an X-ray producing target.

One such X-ray producing betatron is shown in U. 8.,

Patent No. 2,394,072, issued to W. F. Westendorp on February 5, 1946,and assigned to the assignee of the present invention; and a suitableX-ray producing synchrotron is shown in the aforementioned Pollock andWestendorp patent. Since each burst of X rays produced in such betatronsand synchrotrons is small in quantity, it is necessary to directrepeated bursts of X rays toward the moving object for a large intervalof time.

in order that a satisfactory image may be obtained and recorded uponfilm. However, because the object is moving, the X rays must be directedat it stroboscopically; that is, in order to ensure that the X rays willalways be directed toward the moving object at the same point in itscyclically repeating path of movement until a sharp image is recorded onfilm, the occurrence of the X-ray bursts must be synchronized with themotion of the moving ob-. However, the production of X-ray bursts inbetaject. trons and synchrotrons now known to the art is synchronizedwith their power supply frequency, and hereto- I fore there has been noknown means for synchronizing their occurrence with the motion of anobject being radiographed. This situation has existed due to the factthat in a betatron or synchrotron the acceleration of particles can beaccomplished only during the portion of the power supply cycle when themagnetic flux in the magnet is increasing in one direction, from zeroguiding flux at the particle orbit to a maximum. In a biased machinethis occurs over a little less than 180 electrical degrees from zeroflux, or a half cycle of the alternating current power supplypotentiaLand in an unbiased machine overv a little less than electricaldegrees, or a quarter cycle of the alternating current power supplypotential. The

injection of particles during the accelerating cycle must in the art tovary the energy of the particle accelerator output by varying theacceleration time. The present invention uses this adjustment togetherwith a novel method and apparatus to synchronize the occurrence of theX-ray bursts from a betatron or synchrotron with a moving object.

It is, therefore, one object of this invention to provide a method andapparatus for synchronizing the output of a particle accelerator withany given frequency.

It is another object of this invention to provide a meth- I 0d andapparatus for synchronizing an X-ray output from a particle acceleratorwith the motion of a recurrently moving object so as to enable aradiograph of said object to be made.

Other objects and advantages will appear as the description of theinvention proceeds.

In accordance with the invention, a method is disclosed forsynchronizing the output pulses of a betatron or synchrotron with therepetitive movement of an object, while maintaining the acceleratingcycles of the machine synchronous with the supply voltage of itsalternating cur- A rent field. This is accomplished by deriving electricsignal pulses synchronous with the moving object, injecting particles tobe accelerated in the particle accelerator only during an acceleratingcycle and within a given time interval after the beginning of one ofsaid signal pulses, deriving an output, such as X rays, from the machineat Patented Dec. 3, 1957- the end of said time interval, and irradiatingthe object and an X ray sensitive film with the X rays so as to make apicture of a portion of the object. The apparatus for practicing theabove method comprises a gating switch activated for a given timeinterval or duration by first signal pulses synchronous with therepetitive movement of the object past a given point, and a coincidenceswitch receptive of both (1) second signal pulses which are synchronouswith said accelerating cycles, and (2) the output of the gating switch.If the second signal pulses occur during the given time intervals whenthe gating switch is operating, they pass through the coincidence switchand serve to inject particles into the particle accelerator. The gatingswitch output is also used to generate an ejection signal pulse at thetermination of each time interval for causing any particles in theaccelerator to strike an X-ray emitting target. If desired, theapparatus may be modified by also feeding the pulse signal output of thecoincidence switch through a second gating switch to a secondcoincidence switch. The second coincidence switch also receives theejection pulse output of the first named gating switch. Only when thetwo inputs to the second coincidence switch coincide does this switchpermit an ejection pulse to pass, thereby insuring that ejection pulseswill pass only when particles have been injected and accelerated.Moreover, by varying the time of the intervals of given duration inaccordance with any variation in speed of the moving object, exactsynchronization between the particle accelerator output and said movingobject can be attained. The achievement of such a synchronization hasmade it possible to use high powered X-ray machines to scan any fastmoving object stroboscopically, and make a radiograph or even a motionpicture thereof. Such an ability to photograph enclosed moving objectsis of extremely great importance in that it now becomes possible for thefirst time to observe the causes of failure within any motor or pump,for example, without opening the motor or pump.

The features of this invention which are believed to be novel andpatentable are pointed out in the claims which form a part of thisspecification. For a better understanding of the invention, reference ismade in the following description to the accompanying drawings, whereinlike parts are indicated by like reference numerals, in which:

Fig. 1 is a circuit diagram showing one embodiment of the invention;

Fig. 2 is a circuit diagram showing a second embodiment on theinvention; and

Fig. 3 comprises seven graphs showing the wave forms appearing atvarious portions of the circuits of Figs. 1 and 2.

Referring now to Fig. 1, there is shown the basic elements of the novelapparatus needed for practicing the novel method of this invention. Inthis figure, a block 1 is shown, which block may be a motor containingtherein an object having a recurrent motion which it is desired to studystroboscopically by means of X-rays. An X-ray betatron or synchrotron 2is also shown for producing an X-ray beam 3 which irradiates the movingobject to produce upon a film 4 a picture thereof. The moving object isconnected to a shaft 5 to which is aflixed a disk 6 having a tooth 7thereupon. This disk is not permanently afiixed to shaft 5 but may beloosened and turned relative thereto, and then fixed in position.Disposed opposite tooth 7 is a permanent magnet core 8 having a winding9 thereabout for producing a voltage every time tooth 7 is adjacentthereto and cuts through the lines of fiux of said magnetic core. Core 8and its winding 9 may be replaced by a magnetic pick up impulsegenerator such as is made by Electro Products Laboratories, Inc., ofChicago, Ill., for example. There is, therefore, produced in winding 9 avoltage wave form whenever tooth 7 passes core 8, and this voltage isrecurrent and synchronous with the motion of the recurrently movinginject particles therein.

object. The circuits shown within a pair of blocks 11 and 12 are used tosynchronize the output of X-ray betatron or synchrotron 2 with thevoltages produced in the winding 9. The circuit of block 11 comprises agating switch, while the circuit of block 12 comprises a coincidenceswitch. Gating switch 11 is triggered by said voltages and producessquare wave pulses synchronous with the repetitive movement of themoving object, each of which has a given duration. These square wavesare fed into the coincidence switch of block 12. Also fed into saidcoincidence switch are pulses from the X-ray betatron or synchrotronwhich are synchronous with the accelerating cycles of this machine andindicate the proper time to A coincidence between any of the last namedpulses and any of the square waves causes the coincidence switch ofblock 12 to produce an output for causing particles to be injected intothe X-ray betatron or synchrotron and be accelerated therein. At the endof each square wave from the gating switch of block 11, a pulse isproduced for ejecting any accelerated particles in the X-ray betatron orsynchrotron and causing them to strike an X-ray target and emit theX-ray beam 3. It will thus be apparent that the system shown in Fig. 1causes the moving object to be irradiated synchronously with themovement thereof, while the accelerating cycle of the X-ray betatron orsynchrotron remains synchronous with the frequency of its supplyvoltage. A more detailed description of the elements of Fig. 1 and theirexact mode of operation now follows.

The voltages induced in coil 9 are differentiated in a differentiatingnetwork which includes a capacitor 13 coupled between one end of saidcoil and a resistor 14, the other end of said coil being connected toground. The resultant :sharp signal pulses are pictured in Fig. 3b andlabelled B. Pulses B in Fig. 3b are obtained by means of a modificationof Fig. 1 that is shown in Fig. 2, and will be explained below. Pulses Bare then fed into the gating switch 11, which may comprise a one-shotmultivibrator 15. This multivibrator includes a triode 16 which isnormally conducting due to a positive po tential applied to its controlgrid through a resistor 17 coupled to a positive terminal 18 of a sourceof potential. Multivibrator 15 also includes a triode 19 having itscathode coupled to the cathode of tube 16, both cathodes being coupledto ground through a common resistor 21. The bias developed acrossresistor 21 due to the conduction of current therethrough by normallyconducting tube 16 serves to maintain tube 19 normally nonconducting. Asis usual in such one-shot multivibrators, the anode of tube 19 iscoupled through a capacitor 22 to the control grid of tube 16, and theanode of tube 16 is coupled through a resistor 23 to the control grid oftube 19. The anodes of tubes 16 and 19 are also coupled throughrespective anode resistors to positive terminal 18 of the source ofpotential. A positive pulse B is applied to the control grid of normallynon-conducting tube 19, and causes it to conduct; whereupon its anodepotential drops in a negative direction, producing a negative goingvoltage pulse. This negative voltage pulse is transmitted throughcapacitor 22 to the control grid of tube 16 and serves to cut 01fnormally conducting tube 16 and thereby produce in this latter tube aresultant rise in anode potential. The anode of tube 16 will remain atits positive peak for the interval of time that it takes the charge uponcapacitor 22 to leak off through resistor 17 and the anode resistor oftube 19, after which time the control grid of tube 16 will again becomesufficiently positive to cause this tube to conduct. Conduction of tube16 then produces a negative pulse that is transmitted through resistor23 to the control grid of tube 19 to cut off this latter tube andre-establish the original condition wherein tube 16 is normallyconducting and tube 19 normally nonconducting. The resultant potentialrise at the anode of tube 16 has the form of a square wave and isdepicted in Fig. 3c as wave forms C. Similar square waves are alsoproduced simultaneously at the anode of tube 19, but these waves arenegative in polarity. The negative going square wave output of tube 19is applied to a dilferentiating network comprising a capacitor 24 and aresistor 25, and the resultant diiferentiated signal pulses, having awave shape shown in Fig. 3d, are supplied through a conductor 26 to theX-ray producing device 2. The positive going voltage pulses of thediiferentiated output signal of tube 19 are indicated at D in Fig. 3d.

The positive square wave signal C from the anode of tube 16 is appliedto the third grid of a coincidence switching tube 27 through a couplingcapacitor 28. Tube 27 has five grids therein of which the second andfourth are connected together and the fifth is connected to the cathodethereof. Applied to the control grid of tube 27 by a lead 29 through acapacitor 31 is a series of signal pulses labelled A and shown in Fig.311. Both the control grid and the third grid respectively of tube 27have negative biases applied thereto through respective resistors 32 and33 which are connected to a negative terminal 18 of the :supply voltage.The cathode of tube 27 is connected to ground, the second and fourthgrids are connected to the positive source of potential through positiveterminal 18, and the anode is also connected to the terminal 18 of thepositive source of potential through an anode resistor. Theaforementioned negative biases upon the first and third grids of tube 27are so chosen that this tube can only conduct when'a positive pulse Afrom lead 29 coincides with a positive square wave C from the anode oftube 16. Upon the conduction of tube 27, a negative pulse is produced inits anode circuit which is coupled through a capacitor 34 to a lead 35;this negative pulse is depicted in Fig. 3e and is labelled E. Anexamination of Figs. 3a to Be will readily disclose that pulse E on lead35 coincides with a pulse A on lead 29 and only appears when this latterpulse coincides with a square wave C. Each square wave C of course isstarted by a pulse B coincident with the moving object. Further, pulse Dalso coincides with the termination of the aforementioned square wave C.

Leads 26, 29 and 35 are respectively connected to an. ejection circuit36, an injection timing circuit 37, and an injection circuit 38 of X-raybetatron or synchrotron.- 2. The betatron and synchrotron may be thoserespectively noted above as being shown in the Westendorp 2,394,072patent and the Pollock and Westendorp patent. The injection timingcircuit 37 is used to derive the pulses A which serve as injectiontiming pulses timed with respect to the zero fiux time of the betatronor synchrotron, as is explained in the aforementioned article by T. W.Dietze and the present inventor. Such pulses may be obtained by placinga peaker strip in a betatron as shown in U. S. Patent No. 2,553,305,issued to the present inventor on May 15, 1951 and assigned to theassignee of the present invention. The use of a peaker strip in asynchrotron to obtain such injection timing pulses is disclosed in theaforementioned Pollock and Westendorp patent.

Lead 35 is connected to the injection circuit 38 of the betatron orsynchrotron and serves to couple negative injection trigger pulses E, tosaid injection circuit. These negative pulses are timed with respect tothe zero flux condition previously noted, and cause particles to beinjected into the betatron or synchrotron to be accelerated therein.Suitable injection circuits activated by negative pulses for both thebetatron and synchrotron are respectively shown in the aforementionedpatent to the present inventor and in the Pollock and Westendorp patent.

As noted above, pulses D are fed by lead 26 into an ejection circuit 36of the betatron or synchrotron. This ejection circuit responds only tothe positive pulses D of the pulses shown in Fig. 3d and serves to causethe accelerated particles to strike an X-ray emitting target in responsethereto. These X-rays are shown as beam 3,

and they are directed through moving object 1 to strike film 4 andproduce a radiograph. Suitable ejection circuits for a synchrotron and abetatron are respectively shown in the aforementioned Pollock andWestendorp patent and in Westendorp Patent 2,394,072.

Examining now Figs. 1 and 3 in order to explain the operation of theinvention, it will be apparent that synchronizing pulses B derived frommoving object 1 have a different frequency than injection timing pulsesA derived from injection timing circuit 37, which latter pulses aresynchronized with the aforementioned accelerating cycles. Pulses B areused to generate positive square waves C, and also negative square wavesfrom which positive pulses D can be derived. The square waves have agiven time duration which is preferably slightly less than one-quarterof the period of time between pulses A if the particle accelerator isunbiased and slightly less than one-half said period if the acceleratoris biased, thus ensuring against accidental ejection due to contractionof the particle stream at the end of an acceleration cycle. Positivesquare waves C serve as injection gate pulses for coincidence tube 27,insuring that this tube will only conduct when injection gate pulses Cand injection timing pulses A coincide. Upon this coincidence, aninjection trigger pulse E is produced to cause particles to be injectedin the betatron or synchrotron so that they can be accelerated thereby.Consequently, it will be apparent that particles are injected in thebetatron or synchrotron only when an injectigp timing pulse A from theinjection timing circuit occurs within said given time interval after asynchronizing pulse B. A short time thereafter, at the end of said giveninterval of time, a pulse D appears upon lead 26 and causes theaccelerated particles to strike the X-ray target. The interval betweenpulse D and pulse A is labelled x and corresponds to the accelerationtime of the particle in the betatron or synchrotron.

From the foregoing it will be apparent that the present invention hasmade it possible to synchronize the motion of a moving object with theoutput of an X-ray betatron or synchrotron without changing theaccelerating cycle synchronization of the betatron or synchrotron withits flux supply voltage. This feature has made it possible to obtaininternal stroboscopic radiographs of machines having recurrently movinginternal objects. Further, by successively moving disk 6 relative tomoving object 1 on shaft 5 and then fixing its position, thussuccessively shifting the phase of pulses B, successive points of aninternal moving part can be stroboscopically radiographed and theresults can then be placed upon a continuous film to provide a motionpicture of the movement of the object.

While the circuit and method disclosed in Fig. 1 enables the foregoingadvantages to be obtained, it will be noted that the ejection circuit 36is pulsed by the first pulse D even when no injection trigger pulse E ispresent to inject particles into the betatron or synchrotron. Thispulsing of the ejection circuit, while it has no elfect on the X-rayoutput, may have a deleterious effect upon the ejection circuit powersupply in that excessive current flow may ensue with resultant damage tothe equip ment. To prevent this condition, the circuit of Fig. 1 hasbeen modified in the manner shown in Fig. 2 by the addition of a secondone-shot multivibrator gating switch 39 and a second coincidence switchtube 41. Corresponding elements in Figs. 1 and 2 are correspondinglynumbered and perform the same functions in the same way. In Fig. 2, whencoincidence switch tube 27 conducts to provide an injection triggerpulse E for in-- jection circuit 38, this negative pulse is now alsoconducted through a rectifier 43 and a capacitor 44 to the control gridof a normally conducting triode 45 of multivibrator gating switch 39.Tube 45 has a positive bias applied to its control grid by a resistor 42coupled to the positive terminal 18 of the source of potential, and thecathode of this tube is coupled to the cathode of a tube 46 of themultivibrator, both cathodes being coupled to ground through a resistor47. The current flow through normally conducting tube 45 develops apotential across cathode resistor 47 which serves to bias tube 46 tocutoff so that this latter tube is normally nonconducting. The anode oftube 46 is connected to the control grid of tube 45 through theaforementioned capacitor 44, and the anode of tube 45 is connected tothe control grid of tube 46 through a resistor 48. Tubes 45 and 46respectively correspond to tubes 16 and 19 of multivibrator and operatein exactly the same Way. The anode of tube 45 is coupled through acapacitor 49 to the third grid of a five grid second coincidence switchtube 41. The grids of tube 41 are connected in the same way as thosepreviously described in connection with first coincidence tube 27, andthe cathode of tube 41 is grounded. A negative bias is applied to therespective first and third grids of tube 41 by means of resistor and aresistor 51 which are coupled to negative terminal 18 of the source ofpotential. The anodes of tubes 41, 45 and 46 are connected throughrespective resistors to the source of potential at positive terminal 18.A capacitor 52 is connected to the anode of tube 41 and serves to coupleany output therefrom through a phase inverter 53 such as a transformer,to lead 26 and ejection circuit 36. Since the anode of tube 16 isconnected through capacitor 28 to the third grid of tube 27, it will beseen that multivibrator 15 and coincidence tube 27 operate in thisfigure in exactly the same manner as they did in Fig. 1 to produce aninjection trigger pulse E on lead whenever an injection timing pulse Aappears on lead 29 that coincides with the square wave C generated bysynchronizing pulse B from the moving object. However, the pulseappearing on lead 26 and activating the ejection circuit 36 is no longerpulse D, as will be described below.

Now will be described the operation of the abovementioned portions ofFig. 2 which differ from Fig. l. The negative injection trigger pulse Ederived from the anode of tube 27 and depicted in Fig. 3e passes throughrectifier 43 and capacitor 44 and serves to cut off normally conductingtube 45 and thereby causes normally nonconducting tube 46 to conduct dueto multivibrator action. A resultant positive square wave appears at theanode of tube 45 having a duration determined by the rate of dischargeof capacitor 44 through resistor 42 and the anode resistor of tube 46,and a similar negative square wave appears simultaneously at the anodeof tube 46, rectifier 43 having a polarity such that this negativesquare wave cannot pass therethrough and to injection circuit 38. Thispositive square wave is depicted in Fig. 3 and labelled F, and it onlycan occur when an injection trigger pulse E has simultaneously gone toinjection circuit 38 and caused particles to be injected into thebetatron or synchrotron 2. Positive square wave F will cause coincidencetube 41 to conduct only when a positive pulse D, derived from thenegative square wave at the anode of tube 19, is produced andsimultaneously applied to the control grid of tube 41. At this time,tube 41 conducts to produce a negative pulse G depicted in Fig. 3g, andthis negative pulse then passes through capacitor 52 to be reversed inpolarity by phase inverter 53 and applied as a positive pulse to lead 26and ejection circuit 36 of the betatron or synchrotron. It will be seenfrom the operation of Fig. 2 described above and from Fig. 3 that now anejection trigger pulse G for causing accelerated particles to strike theX-ray target only can occur when particles have actually been injectedinto the betatron synchrotron and have been accelerated. The time xbetween waveforms E and G is the accelerating period of particles in thebetatron or synchrotron and it determines the amount of acceleration ofthese particles. This time equals the time x betweern waveforms A and Dsince the former ejection pulse D coincides with pulse G, but now anejection pulse G is produced only when particles are injected, thuseffectively eliminating the deleterious effects of the first occurringpulse D in Fig. 3a.

The circuit of Fig. 2 also differs from that of Fig. 1 in one otherrespect. The above discussion in connection with Figs. 1, 2 and 3proceeded upon the assumption that moving object 1 was moving at anearly constant speed, whereupon tooth 7 of disk 6 would pass core 8 atregular intervals and the same point on moving object 1 would beperiodically scanned by X-ray beam 3. However, under actual operatingconditions, the speed of the moving object may easily vary by more than1 or 2 percent of its normal speed, causing the image upon film 4 to beslightly blurred due to the fact that different points of the movingobject are being scanned. In order to compensate for any speed variationin moving object 1, a further modification has been made in Fig. 2. Asecond tooth 10 has been added to disk 6 and a triode 20 has beeninserted between differentiating network 13, 14 and multivibrator 15with the control grid of tube 20 being connected to the junction ofcapacitor 13 and resistor 14. The tube 20 is self biased to cut-off bymeans of a resistor 30 and a capacitor 40 which couple its cathode toground, and its anode is coupled to the positive terminal 18 of thesource of potential through a esistor 50. The anode of: tube 20 is alsoconnected to a pair of rectifiers 54 and 55, rectifier 54 beingconnected to the anode of normally conducting tube 16 of multivibrator15, and rectifier 55 being connected to the anode of normallynonconducting tube 19 of said multivibrator. Also, in order to speed theaction of this multivibrator, a capacitor 56 has been placed acrossresistor 23 between the anode of tube 16 and the control grid of tube 19which is coupled to ground through a resistor 57. The values ofcapacitor 22, resistor 17, and the anode resistor of tube 19 are sochosen that the square wave produced by multivibrator 15 now exceedsslightly the electrical degrees time interval previously noted if usingan unbiased X-ray betatron or synchrotron, or slightly exceedselectrical degrees if the machine is biased.

Now will be described the operation of the last mentioned portions ofFig. 2 which differ from Fig. 1. Assuming a counterclockwise rotation ofdisk 6, when tooth 7 cuts the line of flux of core 8, a potential isinduced in winding 9 which is differentiated by capacitor 13 andresistor 14 to produce a positive pulse B, as shown in Fig. 3b, which issuflicient to overcome the bias of tube 20 and cause this tube toproduce a negative pulse at its anode. Due to the high positivepotential at the anode of normally nonconducting tube 19, this negativepulse passes through rectifier 55 to the anode of tube 19 and thenthrough capacitor 22 to the control grid of normally conducting tube 16,causing this tube to be cut off. Because normally conducting tube 16 hasa low anode potential, this negative pulse cannot pass through rectifier54 to the anode of tube 16, and therefore tube 19 is unaffected thereby.When normally conducting tube 16 is caused to be cut off by the saidnegative pulse, due to multivibrator action, tube 19 is then caused toconduct. With the triggering of multivibrator 15, as previouslydescribed, particles to be accelerated will be injected by injectioncircuit 38 into the X-ray betatron or synchrotron 2 if a pulse A occursduring the interval when multivibrator 15 is in operation. Now however,instead of supplying an ejection trigger pulse G at the naturalconclusion of multivibrator square wave output C, the multivibratoraction is terminated when tooth 10 cuts the lines of flux of core 8. Thepositive pulse generated when tooth 10 is opposite core 8 is depicted inFig. 3b and labelled B. Pulse B causes a negative pulse to appear at theanode of tube 20 and since tube 19 is now conducting and tube 16 is nowout off, the above described action of these tubes is reversed and thisnegative pulse can only affect tube 19, while it can have no effect upontube 16. Pulse B, therefore, serves to operate the multi vibrator andrestore the original condition where tube 16 is conducting and tube 19is nonconducting. It will thus be apparent that by means of tooth 10, ifthe motion of moving object 1 speeds up, square wave C will have ashorter duration than if moving object 1 slows down, in view of the factthat pulse B will occur closer or farther away from pulse B. Since thetermination of the square wave C determines the time when ejectiontrigger pulse G will cause the accelerated particles to strike an X-raytarget and emit an X-ray beam 3, it will be apparent that X-ray beam 3is now perfectly synchronized with any speed variation in movingobject 1. Thus it is now possible to insure against any blurring of theimage of the moving object upon film 4.

In connection with Figs. 1 and 2, it should be understood that if sodesired an X-ray integrator may be placed behind film 4 to determinewhen the film has been sufficiently exposed to the X rays to produce apicture. Such integrators are well known in the art, one such suitableinstrument being called the Integron IV and being manufactured by theVictoreen Instrument Co. of Cleveland, Ohio. The output of the X-rayintegrator when the picture is complete may be used to turn off theparticle accelerator until a new film 4 can be placed in position totake a new picture; said output may also be used to turn slightly disk 6with respect to shaft and insert a new film 4 in addition to turning offparticle accelerator 2, thus automatically providing a motion picturerecord of the moving object 1.

It should be understood that the present invention is not limited to anyparticular type of particle accelerator, since any particle acceleratorthat is synchronized with a separate supply voltage can be .adapted foruse with this invention. Further, this invention is not limited to anyparticular device for obtaining synchronizing pulses, since any devicewhich will follow any type of recurrent motion of a moving object can beused to derive suitable synchronizing pulses, regardless of whether themotion is circular or reciprocal. Moreover, the present invention is notlimited to any particular type of switching arrangement but can utilizeany circuits which will insure that only injection timing pulsesoccurring a short time before the ejection pulses will be permitted topass through and inject particles into a betatron or synchrotron, andthat the particles will be ejected at the conclusion of said time.

From the foregoing it is believed apparent that a novel method andapparatus have been disclosed which make it possible for the first timeto study the movements of enclosed moving objects by means of X-raybetatrons or synchrotrons without changing the synchronization of thesepieces of apparatus with their power supply.

While there have been described what are at present considered preferredembodiments of the invention, it will be obvious to those skilled in theart that various changes and modifications may be made therein withoutdeparting from this invention; and it is aimed in the appended claims tocover all such changes and modifications as fall within the true spiritand scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. Apparatus for deriving output pulses from a particle accelerator thatare synchronous with input pulses of a first frequency, said particleaccelerator having an accelerating cycle which recurs at a rate equal toa second frequency, comprising means for injecting particles to beaccelerated into said particle accelerator only during an acceleratingcycle and within a given time interval after the beginning of an inputpulse, and means for deriving an output pulse from the acceleratedparticles at the end of said given time interval.

2. The apparatus of claim 1, further including means for varying theduration of said given time interval in accordance with any variation ofsaid first frequency.

3. The apparatus of claim 1, wherein said particle ac celerator includesan X-ray target, and said means for deriving an output pulse includesmeans for directing the accelerated particles against said X-ray targetto produce Xrays.

4. Apparatus deriving output pulses from a particle accelerator that aresynchronous with input pulses of a first frequency, said particleaccelerator having an accelerating cycle which recurs at a rate equal toa second frequency, comprising means for generating a series ofinjection pulses each of which respectively occurs during a respectiveaccelerating cycle, means for injecting particles to be accelerated intosaid particle accelerator by means of said injection pulses only when aninjection pulse occurs within a given time interval after the beginningof an input pulse, and means for deriving an output pulse from theaccelerated particles at the end of said given time interval.

5. Apparatus for deriving output pulses from a particle accelerator thatare synchronous with a first frequency, said particle accelerator havingan accelerating cycle which recurs at a rate equal to a secondfrequency, comprising means for generating a series of pulses having afrequency equal to said first frequency, means for injecting particlesto be accelerated into said particle accelerator only during anaccelerating cycle and within a given time interval after the beginningof a pulse in said series of pulses, and means for deriving an outputpulse from the accelerated particles at the end of said given timeinterval.

6. Apparatus for deriving output pulses from a particle accelerator thatare synchronous with a first frequency, said particle accelerator havingan accelerating cycle which recurs at a rate equal to a secondfrequency, comprising means for producing a first series of pulseshaving a frequency equal to said first frequency, means for producing asecond series of pulses having a frequency equal to said secondfrequency and each pulse of which respectively occurs during arespective accelerating cycle, means for injecting particles to beaccelerated into said particle accelerator by means of said secondseries of pulses only when a pulse of said second series of pulsesoccurs within a given time interval after the beginning of a pulse insaid first series of pulses, and means for deriving an output pulse fromthe accelerated particles at the end of said given time interval.

7. Apparatus for making stroboscopic radiographs of an object movingrecurrently at a first frequency by means of an X-ray producing particleaccelerator having an accelerating cycle which recurs at a rate equal toa second frequency, comprising means for generating a series of pulseshaving a frequency equal to said first frequency, means for injectingparticles to be accelerated into said particle accelerator only duringan accelerating cycle and within a given time interval after thebeginning of a pulse in said series of pulses, means for directing theaccelerated particles at the end of said given time interval against anX-ray target to produce X rays, and means for recording the X-ray imageof said object when said X rays are directed thereat.

8. The apparatus of claim 7, further including means for varying theduration of said given time interval in accordance with any variation ofsaid first frequency.

9. The apparatus of claim 7, wherein a pulse of said series of pulsesoccurs whenever a point on said moving object passes through a givenpoint in space, and further including means for varying the phase ofsaid series of pulses relative to said point on said moving object.

10. The apparatus of claim 9, further including means for varying theduration of said given time interval in accordance with any variation ofsaid first frequency.

11. Apparatus for making stroboscopic radiographs of an object movingrecurrently at a first frequency by means of a particle acceleratorhaving an accelerating cycle which recurs at a rate equal to a secondfrequency, said particle accelerator including ejection means fordirecting accelerated particles at an X-ray target to produce X rays,comprising means for producing a first series of square Wave pulseshaving a frequency equal to said first frequency, each of said squarewaves having a given time duration, means for producing a second seriesof pulses having a frequency equal to said second frequency and eachpulse of which respectively occurs during a respective acceleratingcycle, means for injecting particles to be accelerated into saidparticle accelerator by means of said second series of pulses only whena pulse of said second series of pulses coincides with any square waveof said first series of pulses, means for producing a third series ofpulses respectively coinciding with the termination of the respectivesquare waves of said first series of pulses, means for activating saidejection means in response to said third series of pulses to irradiatesaid object by means of X rays, and means for recording the X-ray imageof said object.

12. The apparatus of claim 11, wherein the accelerated particles aredirected toward the X-ray producing target only by pulses of said thirdseries of pulses occurring at the termination of the square waves thatcoincide with the pulses of said second series of pulses.

13. The apparatus of claim 11, further including means for producing afourth series of square wave pulses each of which is generated only whena pulse of said second series of pulses coincides with a square wave ofsaid first series of pulses, and means for activating said ejectionmeans in response to said third series of pulses only when a pulse ofsaid third series of pulses coincides with a pulse of said fourth seriesof pulses.

14. The apparatus of claim 13, further including means for varying saidgiven time interval in accordance with any variation of said firstfrequency.

15. The apparatus of claim 13, wherein a pulse of said first series ofpulses occurs Whenever a point on said moving object passes through agiven point in space, and further including means for varying the phaseof said first series of pulses relative to said point on said movingobject.

16. The apparatus of claim 15, further including means for varying theduration of said given time interval in accordance with any variation ofsaid first frequency.

17. The apparatus of claim 14, wherein said moving object is coupled toa disk having at least one tooth thereon and each pulse of said firstseries of pulses is generated only when said tooth passes through agiven point in space, the coupling of said disk relative to said movingobject being such that said disk can be advanced to vary the phase ofsaid first series of pulses.

18. The apparatus of claim 17, further including a second tooth uponsaid disk for producing a fifth series of pulses synchronous with saidfirst frequency but respectively separated in time from the beginning ofthe respective pulses of said first series of pulses for changing theduration of said given time interval in accordance with any variation ofsaid first frequency.

19. Apparatus for making stroboscopic radiographs of an object movingrecurrently at a given frequency by means of a particle acceleratorhaving an accelerating cycle which recurs at a rate equal to anotherfrequency, said particle accelerator including ejection means fordirecting accelerated particles at an X-ray target to produce X rays,comprising means for producing a first series of pulses having afrequency equal to that with which a given point on the moving objectpasses a given point in space, square wave generator means receptive ofand responsive to said first series of pulses for producing a secondseries of square wave pulses having a frequency equal to that of saidfirst series of pulses, means for producing a third series of pulseshaving a frequency equal to the accelerating cycle recurrence rate ofsaid particle accelerator and each pulse of which respectively occursduring a respective accelerating cycle, coincidence switch meansreceptive of said second and third series of pulses for passing only thepulses of said third series of pulses that coincide with pulses of saidsecond series of pulses, the pulses so passed being coupled to saidparticle accelerator and serving to inject therein particles to beaccelerated, means for deriving from said second series of pulses afourth series of pulses which respectively coincide with the terminationof the respective square waves of said second series of pulses foractivating said ejection means to produce X rays for irradiating saidmoving object, and means for recording the X-ray image of said object.

20. The apparatus of claim 19, further including square wave generatormeans receptive of and responsive to the pulses of said third series ofpulses that are passed by said coincidence switch for producing a fifthseries of square wave pulses, and coincidence switch means disposedbetween the means for deriving said fourth series of pulses and saidejection means and receptive of and responsive to both said fourth andfifth series of pulses for only passing those pulses of said fourthseries of pulses that coincide with square waves of said fifth series ofpulses, only the pulses so passed serving to activate said ejectionmeans.

21. The apparatus of claim 19, further including means for generating aseries of pulses equal in frequency to that of first series of pulsesbut separated therefrom by intervals of time which vary in accordancewith any variation in speed of said moving object for terminating theduration of each square wave of said second series of pulses.

22. In combination: X-ray particle accelerator means with anaccelerating cycle which recurs at a rate equal to a given frequency andhaving injection timing circuit means for generating a first series ofelectrical pulses having a frequency equal-to its accelerating cyclerecurrence rate and each pulse of which respectively occurs during arespective accelerating cycle, injection circuit means responsive toelectrical pulses for injecting particles to be accelerated therein, andejection circuit means responsive to electrical pulses for causingaccelerated particles to strike an X-ray target; means for producing asecond series of electrical pulses having a frequency equal to that withwhich a given point on a recurrently moving object passes a given pointin space, one-shot multivibrator means receptive of and responsive tosaid second series of pulses for producing a third series of square waveelectrical pulses having a frequency equal to that of said second seriesof pulses, coincidence tube switch means receptive of said first andthird series of pulses for passing only the pulses of said first seriesof pulses that coincide with square wave pulses of said third series ofpulses, the pulses so passed being coupled to and activating saidinjection circuit means of said X-ray particle accelerator,differentiating means for deriving from said third series of pulses afourth series of electrical pulses which respectively coincide with thetermination of the respective square waves of said third series ofpulses and being coupled to and activating said ejection circuit meansto produce X rays for scanning said moving object, and means forrecording the X-ray image of said object.

23. The apparatus of claim 22, further including oneshot multivibratormeans receptive of and responsive to the pulses of said first series ofpulses that are passed by said coincidence tube switch means forproducing a fifth series of square wave electrical pulses, andcoincidence tube switch means disposed between said differentiatingmeans and said ejection circuit means and receptive of and responsive toboth said fourth and fifth series of pulses for only passing thosepulses of said fourth series of pulses that coincide with square wavesof said fifth series of pulses, only the pulses so passed serving toactivate said ejection circuit means.

24. The apparatus of claim 23, further including means coupled to thefirst-named multivibrator means for generating a sixth series ofelectrical pulses equal in frequency to that of said second series ofpulses but separated therefrom by intervals of time which vary inaccordance with any variation in speed of said moving object and forterminating the operation of said first-named multivibrator means tovary the duration of each square wave of said third series of pulses.

25. The apparatus of claim 24, wherein the means for generating saidsecond series of pulses and the means for generating said sixth seriesof pulses comprise a rotatable disk coupled to said moving object andhaving a pair of teeth thereupon, and magnetic pick-up means disposedadjacent to said disk for producing a pulse each time a tooth of saiddisk passes thereby.

References Cited in the file of this patent UNITED STATES PATENTSStrauss et al Feb. 13, 1940 Westendorp Feb. 5, 1946 Wideroe Dec. 12,1950 Dickinson May 15, 1951 Powell Jan. 20, 1953 Wright et al. May 25,1954 OTHER REFERENCES Electronics Applied to the Betatron, Dietz andDickinson Proceedings of the I. R. E., pgs. 1171-1178.

